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Analyses multi-échelles du comportement en fluage d'alliages de zirconium

Abstract : Zirconium alloys are used in the nuclear industry as fuel cladding tubes in order to prevent radionuclide leaks into primary loop. They are also used to ensure an efficient heat transfer between nuclear fuel and primary water. Under operating conditions, these alloys are subjected to intense thermal-mechanical and neutronic sollicitations. The mechanical wear of fuel rods is a key element in nuclear reactor safety. During this work, TEM investigations have been carried out by coworkers in order to quantify driving plasticity mechanisms in investigated stress and temperature range. The main result of this study is that the prismatic glide of screw dislocations remains the main plasticity mechanism. It is frequently associated with a cross slip mechanism on pyramidal planes. These experimental observations have been implemented into a multiscale approach, thus providing a better description of the phenomenon. The results of a characterization campaign of the multiaxial creep behavior at 400°C of recrystallised Zircaloy-4 are used in this work and a micromechanical interpretation is proposed. The Elasto-Visco-Plastic (EVP) behavior is also characterized with relaxation tests between 280°C and 430°C. Analysis of experimental results indicates macroscopic effects of dynamic strain ageing. At the same time, Finite Element computations on polycrystalline aggregates were undertaken and a procedure for the statistical estimation of intraphase mean mechanical fields is proposed. For a sufficient number of statistical realizations, it is shown that this estimator allows the precise determination of the analytical solution provided by the self consistent model within the framework of anisotropic elasticity. Thus, this procedure was applied to an EVP medium. It seems that rule allow a good description of numerical observations. However, EVP flow of quasi-elastic crystallographic phases remains difficult to describe. The aim of this PhD is to develop models of EVP behavior of zirconium alloys. Our approach is based on a physical description of driving phenomena. The idea is to obtain a good description of a very pronounced mechanical anisotropy of zirconium alloys. The direct implementation of crystallographic texture and plasticity mechanisms in a polycrystalline model allows a good description of multiaxial creep behavior. For industrial purposes, models are simplified and a mixed yield criterion is proposed to describe yield surfaces simulated with the polycrystal approach. This modelling strategy is finally applied to the behavior of recrystallized Zy-4 at 20 and 400°C. To conclude this work, irradiation effects on mechanical behavior of zirconium alloys have been studied through published works and a micromechanical approach is proposed in order to take into account the micromechanisms responsible for strain under irradiation of zirconium alloys.
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https://tel.archives-ouvertes.fr/tel-00642008
Contributor : Mathieu Priser <>
Submitted on : Friday, November 18, 2011 - 9:38:14 AM
Last modification on : Friday, September 25, 2020 - 3:35:52 AM
Long-term archiving on: : Monday, December 5, 2016 - 11:01:42 AM

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  • HAL Id : tel-00642008, version 2

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Mathieu Priser. Analyses multi-échelles du comportement en fluage d'alliages de zirconium. Mécanique des matériaux [physics.class-ph]. Université de Bretagne Sud, 2011. Français. ⟨tel-00642008v2⟩

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